297 Serialize and Deserialize Binary Tree

Serialization is the process of converting a data structure or object into a sequence of bits so that it can be stored in a file or memory buffer, or transmitted across a network connection link to be reconstructed later in the same or another computer environment.

Design an algorithm to serialize and deserialize a binary tree. There is no restriction on how your serialization/deserialization algorithm should work. You just need to ensure that a binary tree can be serialized to a string and this string can be deserialized to the original tree structure.

For example, you may serialize the following tree

    1
   / \
  2   3
     / \
    4   5

as "[1,2,3,null,null,4,5]", just the same as how LeetCode OJ serializes a binary tree. You do not necessarily need to follow this format, so please be creative and come up with different approaches yourself.

 

Note: Do not use class member/global/static variables to store states. Your serialize and deserialize algorithms should be stateless.

这道题让我们对二叉树进行序列化和去序列化的操作。序列化就是将一个数据结构或物体转化为一个位序列，可以存进一个文件或者内存缓冲器中，然后通过网络连接在相同的或者另一个电脑环境中被还原，还原的过程叫做去序列化。现在让我们来序列化和去序列化一个二叉树，并给了我们例子。先序遍历的递归解法，非常的简单易懂，我们需要接入输入和输出字符串流istringstream和ostringstream，对于序列化，我们从根节点开始，如果节点存在，则将值存入输出字符串流，然后分别对其左右子节点递归调用序列化函数即可。对于去序列化，我们先读入第一个字符，以此生成一个根节点，然后再对根节点的左右子节点递归调用去序列化函数即可

public class Codec {

    // Encodes a tree to a single string.
    public String serialize(TreeNode root) {
        if (root == null)
            return "null";
        return root.val + " " + serialize(root.left) + " " + serialize(root.right);
    }
    
    private int s = 0;
    // Decodes your encoded data to tree.
    public TreeNode deserialize(String data) {
        int e = data.indexOf(" ", s);
        if (e == -1) {
            return null;
        }
        String raw = data.substring(s, e);
        s = e + 1;
        TreeNode node = null;
        if (!raw.equals("null")) {
            node = new TreeNode(Integer.parseInt(raw));
            node.left = deserialize(data);
            node.right = deserialize(data);
        }
        return node;
    }
    
    public static void main(String[] args) {
        Codec codec = new Codec();
        String data = "1 2 3 null null 4 5 ";
        System.out.println(codec.serialize(codec.deserialize(data)));
    }
}

// Your Codec object will be instantiated and called as such:
// Codec codec = new Codec();
// codec.deserialize(codec.serialize(root));